1. Field of the Invention
The present invention relates to a communication device and a method used in a wireless communication system, and more particularly, to a communication device and a method of handling a cell reselection in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (COMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
The UE may measure cell(s) in each paging cycle to obtain a measurement result, when the UE is in an idle mode. Then, the UE may perform a cell reselection operation according to the measurement result. However, a time interval between time instants for obtaining two measurement results may be too long, when the UE uses an extended discontinuous reception (eDRX). For example, an eDRX cycle (e.g., 5 minutes) may be greater than an original maximum paging cycle (e.g., 2.56 seconds). That is, previous measurement results may be obtained 5 minutes ago, when the measurement result is obtained in the eDRX cycle. Thus, the previous measurement results may be useless or outdated for the cell reselection operation.
Thus, how to modify existing cell reselection operation is an important topic to be discussed.